1. Field of the Invention
This invention relates to an engine, and more particularly, an engine lubrication method for a small four-cycle internal combustion engine which is particularly suitable for the use with portable or transportable power tools.
2. Description of the Related Art
U.S. Pat. No. 5,950,590 to Everts et al. and U.S. Pat. No. 6,213,079 to Watanabe disclose a prior art small four-cycle engine construction, which are incorporated herein by reference.
Portable power tools such as line trimmers, blower/vacuums, chain saws are mostly powered by two-cycle internal combustion engines or electric motors. Some transportable power tools such as tiller/cultivators, generators are currently powered by two-cycle or four-cycle internal combustion engines. With the growing concern regarding air pollution, there is increasing pressure to reduce the emissions of both portable and transportable power equipment. Electric motors unfortunately have limited applications due to power availability for corded products, and battery life and power availability for cordless devices. In instances where weight is not an overriding factor such as lawn mowers, emissions can be dramatically reduced by utilizing heavier four-cycle engines. When it comes to power tools such as line trimmers, chain saws and blower/vacuums, four-cycle engines pose a very difficult problem. Four-cycle engines tend to be too heavy for a given horsepower output and lubrication becomes a very serious problem since portable or transportable power tools must be able to run in a very wide range of orientations except generators or tiller/cultivators. For some tiller/cultivators powered by four-cycle engines with vertical power shaft, lubrication also becomes a serious problem since it is difficult to use same lubrication system as engines with horizontal power shaft.
Therefore, it is an object of the present invention to provide a small four-cycle internal combustion engine having low emissions and is sufficiently light weight to be carried and/or transported by an operator, which is especially suitable for a hand-held or transportable power tool.
It is a further object of the present invention to provide a small four-cycle internal combustion engine having an internal lubrication system enabling the engine to be run at a wide variety of orientations typically encountered during normal operation, which is especially suitable for a portable or transportable power tool.
It is a further object of the present invention to provide a small lightweight four-cycle engine having an engine block, an overhead valve train and a lubrication system to splash oil mist to lubricate the crank case throughout the normal range of operating positions, which is especially suitable for a portable or transportable power tool.
It is yet a further object of the invention to provide a return system of lubricant to return lubrication oil into oil reservoir after lubricating parts in the crankcase and the overhead valve chamber.
These and other objects, features, and advantages of the present invention will become apparent upon further review of the remainder of the specification and the accompanying drawings.